I've got the same problem with at least 13.04 and now with 13.10.
I've noticed, that the gnome-screensaver deamon wasn't running after a fresh login. Once the deamon is running, locking after suspend is working again.
I didn't figure out, why this deamon isn't running. However my simple workaround: just add the gnome-screensaver to the session startup list (gnome-session-properties).
I've got the same problem with at least 13.04 and now with 13.10.
I've noticed, that the gnome-screensaver deamon wasn't running after a fresh login. Once the deamon is running, locking after suspend is working again.
I didn't figure out, why this deamon isn't running. However my simple workaround: just add the gnome-screensaver to the session startup list (gnome- session- properties) .